Project background

Decomposing organic waste in landfills generates large quantities of biogas, containing methane (CH4) and carbon dioxide (CO2) both greenhouse gases that contributes significantly to the global problem of climate change. Biogas is a potential renewable energy source due to his high content in methane and can be used for generating power and heat.

Nowadays, Combined Heat and Power engines (CHP engines) are the most often used technology for biogas energy recovery, but microturbines can become an attractive option due to some advantages over CHP engines:

Microturbines are modular elements with power ranges between 30-200 kW and they can be installed in so-called 'multipacks' of several units that can be adapted to any installation size. This means that microturbines can be adapted to low biogas production landfills and to low demand power installations. This represents an advantage over CHP engines, which present power ranges between 300kW-3MW what means that their installation for low biogas production landfills is not technical and economically viable.

Microturbines have lower contaminant emissions than CHP engines. This fact is important in NOx emissions.

Microturbines are compact engines with few mobile elements. For this reason, they have lower maintenance costs than CHP engines.

Microturbines can increase their energy recovery process efficiency by means of the use of a heat recovery element.

Nevertheless, landfill biogas contains some trace compounds that are harmful to energy recovery equipment causing an increase of maintenance costs. Hydrogen sulphide and siloxanes constitute the most important of these contaminants. H2S removal is very important since it is toxic and corrosive to equipment as well as a smelly compound. Combustion of siloxanes produces SiO2, which presents chemical and physical properties similar to those of glass causing important mechanical damages. Therefore, landfill biogas for energy recovery usually needs an upgrading process in order to avoid problems associated to the presence of these trace compounds.

Physical-chemical processes are the most often used methods for biogas cleaning. Nowadays, some biological biofilters for hydrogen sulphide removal can also be found in market. Biological methods have some advantages over physical-chemical methods like that they present the same efficiency, avoid the use of a catalyst, reduce power consume and avoid production of secondary effluents that must be treated.

The most important biotechnological methods are biofilters, bioscrubbers and biotrickling filters. Due to the fact that the last ones, compared to the other technologies, don't present problems of medium acidification, two biological cleaning systems based on a 'biotrickling filter' will be developed: one of them will be used for hydrogen sulphide removal and the other one for siloxanes elimination.

For the demonstration of effectiveness of siloxanes, biofilter we need a proven analysis method for the detection of siloxanes in biogas. Analytical methods used nowadays for siloxanes analysis in biogas resulted in differences in assessment data. With the aim of defining an optimum methodology, the efficiency of different analysis methods will be demonstrated and an improved one will be defined.